Grease copositions

ABSTRACT

A grease composition comprising base oil and as thickener calcium complex soap and lithium soap is disclosed. A higher fatty acid, an aromatic monocarboxylic acid and a lower fatty acid are used as carboxylic acids constituting the calcium complex soap and lithium soap. The grease composition has a high dropping point and excellent shear stability, and exhibits thermal stability and long bearing life.

FIELD OF THE INVENTION

The present invention relates to a grease composition. More specifically, the present invention relates to a heat-stable lithium-containing calcium complex-based grease composition which has a high dropping point and excellent shear stability, and exhibits long bearing life.

BACKGROUND OF THE INVENTION

With the advancement of mechanical technology such as automobiles or electric equipment, operating conditions are using higher temperatures and are getting harsher every year with the minimisation of size and weight and increase in output of various types of equipment. Consequently, there is an increased demand for improved performance of grease for use in various equipment under a high temperature. Grease compositions which have a high dropping point and excellent thermal stability have been proposed.

In addition to the improvement in grease performance under a high temperature, there is also an increased demand for materials and the like which are safe to use for humans and can be produced with less burden on the environment, and consequently greases which meet these requirements are needed. With regard to the requirements, a grease composition which uses lithium complex soap or urea as a thickener exhibits an excellent dropping point and thermal resistance. In order to improve the characteristics, there are various proposals for this kind of grease composition.

Firstly, as a grease composition which uses a lithium soap-based thickener, JP-A-2006-131721 proposes lithium complex grease comprising a lithium salt of an aliphatic monocarboxylic acid, a lithium salt of an aromatic dibasic acid and a lithium salt of an aliphatic dibasic acid, which is a grease that has a better higher dropping point than lithium grease and allows a wider temperature range for use. However, since lithium, which is the starting material of lithium grease, is not limited in its use to grease and is variously used in other fields, there is concern about resource depletion or a steep rise in cost in the future due to a recent increase in demand. In addition, lithium complex grease has problems in that the production procedure is complex and a longer time is required because the reaction of two kinds of aliphatic acid comprises two stages.

In addition, as a grease composition which uses urea as a thickener, JP-A-2008-231310 proposes diurea grease which can be used for a long period of time at a high temperature. However, since an amine compound such as aniline, which is used as the starting material, is extremely toxic, extra care should be taken when handling for production, and therefore there is a safety problem.

Accordingly, in place of grease compositions using lithium soap or urea as a thickener, which are not quite satisfactory from the viewpoints of safety and burdens on the environment, grease compositions using calcium as a thickener have been investigated which have an advantage in terms of production cost in addition to safety and burden on the environment. However, greases using calcium soap as a thickener usually have a poorer dropping point and thermal resistance than lithium grease, lithium complex grease or urea grease, and therefore greases using calcium soap do not meet requirements as grease suitable for current operating conditions.

As greases meeting such requirements, so-called calcium complex greases have been proposed which generally use as a thickener higher fatty acid or lower fatty acid calcium complex soap.

In particular, JP-A-2009-249419 proposes a calcium complex grease having a high dropping point which uses as a thickener calcium soap comprising calcium salts of a dibasic acid and fatty acid. However, there are problems in that a suitable consistency cannot be maintained if the added amount of thickener is small, and there is a restriction in the form of dibasic acid, especially terephthalic acid, which is used as a starting material, and the terephthalic acid has to be introduced at a high temperature of 120° C. for production.

Accordingly, an objective of the present invention is to provide a heat-stable grease composition which comprises a grease that has a thermal resistance equivalent to or higher than greases using lithium soap or urea as a thickener, and has a high dropping point and excellent shear stability, and exhibits long bearing life. As a result of elaborate investigation by the inventors, it was found that the above-mentioned problems can be solved by using lithium soap and calcium soap where a specific higher fatty acid, specific lower fatty acid, and specific aromatic monocarboxylic acid are added.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a grease composition comprising base oil and, as thickener, calcium complex soap and lithium soap, the grease composition being characterised in that a C18-22 straight-chain, substituted or unsubstituted higher fatty acid, a substituted or unsubstituted aromatic monocarboxylic acid having a benzene ring and a C2-4 straight-chain saturated lower fatty acid are used as carboxylic acids constituting the calcium complex soap and lithium soap.

In addition, the grease composition may be obtained by blending 3 to 25 parts by mass of a straight-chain higher fatty acid, 0.5 to 3 parts by mass of an aromatic monocarboxylic acid and 1 to 5 parts by mass of a straight-chain saturated lower fatty acid as base starting materials, based on 100 parts by mass of the total blended amount for the grease composition.

In addition, the grease composition may include a straight-chain higher fatty acid which is at least one selected from stearic acid, oleic acid, 12-hydroxystearic acid and behenic acid, an aromatic monocarboxylic acid which is at least one selected from benzoic acid and p-toluic acid, and a straight-chain saturated lower fatty acid which is at least one selected from acetic acid and butyric acid.

Moreover, the mass ratio (Li/Ca) of the lithium metal content to the calcium metal content in the thickener starting material may be 1 part per 100 to 5 parts per 100.

The method for producing a grease composition may be a method comprising the step of forming lithium-containing calcium complex soap by adding a straight-chain higher fatty acid, an aromatic monocarboxylic acid, a straight-chain saturated lower fatty acid, calcium hydroxide and lithium hydroxide to base oil.

The lithium-containing calcium complex grease composition according to the present invention has a high dropping point and maintains a suitable consistency, and in addition to the fact that the composition can be used under a high temperature environment, which was only possible with lithium-based grease or urea grease in the past, the composition exhibits safety, environmental and low-cost effects. Furthermore, the lithium-containing calcium complex grease composition according to the present invention has excellent shear stability, and exhibits thermal stability and long bearing life.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be described, but the technical scope of the present invention is not limited by the embodiment in any way.

The grease composition of the present embodiment includes “base oil” and “thickener” as essential structural components. Hereinafter, components included in the grease composition, the amount (blended amount) of each component in the grease composition, the method for producing the grease composition, the properties of the grease composition and the use of the grease composition will be described in said order.

Base Oil

The base oil for use in the grease composition of the present embodiment is not particularly restricted. For example, oil used in general grease compositions such as mineral oil, synthetic oil, animal and vegetable oils or mixed oil thereof may be appropriately selected. As specific examples, base oils belonging to Group 1, Group 2, Group 3, Group 4 and the like in the API (American Petroleum Institute) base oil category may be used singly or as a mixture.

Examples of the Group 1 base oil include paraffin-based mineral oils which can be obtained by refining a lubricating oil distillate obtained from an atmospheric distillation of crude oil, by appropriately combining means of solvent refining, hydrotreating, dewaxing or the like. Examples of the Group 2 base oil include paraffin-based mineral oils which can be obtained by refining a lubricating oil distillate obtained from an atmospheric distillation of crude oil, by appropriately combining means of hydrotreating, dewaxing or the like. The Group 2 base oil refined by Gulf's hydrotreating or the like has less than 10 ppm sulphur content and at most 5% aroma content, and may be preferably used in the present invention. Examples of the Group 3 base oil and Group 2 plus base oil include paraffin-based mineral oils which can be manufactured by subjecting a lubricating oil distillate obtained from an atmospheric distillation of crude oil to high hydrogenation refinement, base oils refined by the ISODEWAX process according to which a wax produced by a dewaxing process is converted/dewaxed to isoparaffin, and base oils refined by the Mobil wax isomerisation process, and these oils may also be preferably used in the present embodiment.

Examples of synthetic oil include polyolefins, diesters of dibasic acid such as dioctyl sebacate, polyol esters, alkyl benzenes, alkyl naphthalenes, esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, polyphenyl ethers, dialkyl diphenyl ethers, fluorine-containing compounds (perfluoropolyether, fluorinated polyolefin and the like), silicones and the like. The above-mentioned polyolefins include various olefin polymers and hydrogenated products thereof. Any olefins may be used, and examples include ethylene, propylene, butene, α-olefins having 5 or more carbon atoms and the like. Polyolefins may be produced by using one of the above-mentioned olefins or two or more of them in combination. In particular, so-called poly-α-olefin (PAO) is preferably used as a polyolefin, which is a Group 4 base oil.

Oils synthesised by means of GTL (gas to liquid) by the Fischer-Tropsch process, which is the technology of obtaining liquid fuel from natural gas, have significantly lower sulphur and aroma contents and a significantly higher paraffin component ratio than mineral base oils obtained by refining crude oils, and therefore exhibit excellent oxidation stability and extremely small evaporative loss. Thus, the oils can be preferably used as the base oil of the present embodiment.

Thickener

A thickener used in the present embodiment is lithium-containing calcium complex soap obtained by a plurality of carboxylic acids being reacted with a specific base (typical examples are calcium hydroxide and lithium hydroxide). Herein, the term “complex” in the lithium-containing calcium complex soap according to the present embodiment means that a plurality of carboxylic acids are employed. There are three source carboxylic acids for the lithium-containing calcium complex soap according to the present embodiment, which are (1) higher fatty acid, (2) aromatic monocarboxylic acid and (3) lower fatty acid. Hereinbelow, the carboxylic acid moieties (anion moieties) in the lithium-containing calcium complex soap will be described.

(1) A higher fatty acid for use in the present embodiment is a C18-22 straight-chain higher fatty acid (monocarboxylic acid). Herein, the straight-chain higher fatty acid may be unsubstituted or substituted with one or more substituents (for example, a hydroxyl group or the like). The straight-chain higher fatty acid may be a saturated or unsaturated fatty acid, but is preferably a saturated fatty acid. Specific examples of a saturated fatty acid include stearic acid (octadecanoic acid, C18), tuberculostearic acid (nonadecanoic acid, C19), arachidic acid (icosanoic acid, C20), henicosanoic acid (C21), behenic acid (docosanoic acid, C22) and hydroxystearic acid (C18, hydrogenated castor oil fatty acid), and examples of an unsaturated fatty acid include oleic acid, linoleic acid, linolenic acid (C18), gadoleic acid, eicosadienoic acid, mead acid (C20), erucic acid, docosadienoic acid (C22) and the like. These acids may be used alone or a number of them may be used in combination. For example, in the case of including an unsaturated fatty acid, a saturated fatty acid is preferably used in combination.

(2) An aromatic monocarboxylic acid for use in the present embodiment is a substituted or unsubstituted aromatic monocarboxylic acid having a benzene ring. Herein, the aromatic monocarboxylic acid may be unsubstituted or substituted with one or more substituents (for example, an o-, m- or p-alkyl group, a hydroxy group, an alkoxy group or the like). Specific examples include benzoic acid, methyl benzoic acid {toluic acid (p-, m-, o-)}, dimethyl benzoic acid (xylyl acid, hemellitic acid, mesitylenic acid), trimethyl benzoic acid {prehnitylic acid, durylic acid, isodurylic acid (α-, β-, γ-)}, 4-isopropylbenzoic acid (cuminic acid), hydroxybenzoic acid (salicylic acid), dihydroxybenzoic acid {pyrocatechuic acid, resorcylic acid (α-, β-, γ-), gentisic acid, protocatechuic acid}, trihydroxybenzoic acid (gallic acid), hydroxy-methyl benzoic acid {cresotinic acid (p-, m-, o-)}, dihydroxy-methyl benzoic acid (orsellinic acid), methoxybenzoic acid {anisic acid (p-, m-, o-)}, dimethoxybenzoic acid (veratric acid), trimethoxybenzoic acid (asaronic acid), hydroxy-methoxy benzoic acid (vanillic acid, isovanillic acid), hydroxy-dimethoxy benzoic acid (syringic acid) and the like. These may be used alone or a number of them may be used in combination. In the present specification, alkyl in the “substituent” and alkyl moiety in alkoxy are, for example, 1-4 linear or branched alkyls.

(3) A lower fatty acid (monocarboxylic acid) for use in the present embodiment is a C2-4 straight-chain saturated lower fatty acid. Specific examples include acetic acid (C2), propionic acid (C3) and butyric acid (C4). These may be used alone or a number of them may be used in combination.

Among these, a combination of stearic acid or behenic acid as the straight-chain higher fatty acid, benzoic acid or p-toluic acid as the aromatic monocarboxylic acid, and acetic acid or butyric acid as the lower fatty acid is the most preferred combination from the viewpoints of good texture, viscosity (body), easy production and the like.

Other Thickeners

For the grease composition of the present embodiment, another thickener may also be used in combination with the above-mentioned lithium-containing calcium complex soap. Examples of other thickeners include tricalcium phosphates, alkali metal soaps, alkali metal complex soaps, alkaline earth metal soaps, alkaline earth metal complex soaps (other than calcium complex soaps), alkali metal sulfonates, alkaline earth metal sulfonates, other metal soaps, terephthalamate metal salts, triurea monourethane, diurea, tetra-urea, other polyurea, clay, silica (silicon oxide) such as silica aerogel, or fluorine resins such as polytetrafluoroethylene, and the like. These may be used alone or in combination of two or more kinds. Apart from the listed examples, any substances capable of imparting thickening effects to a liquid substance may be used.

Optional Components

The grease composition of the present embodiment may also include optional additives such as an antioxidant, an anti-rust agent, an oiliness improver, an extreme pressure additive, an anti-wear agent, a solid lubricant, a metal deactivator, a polymer, a metal-based cleaner, a non-metallic cleaner, a colouring agent and a water repellent agent, where the total amount of optional components is about 0.1 to 20 parts by mass based on 100 parts by mass of the total grease composition. Examples of an antioxidant include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-para-cresol, p,p′-dioctyldiphenylamine, N-phenyl-α-naphthylamine, phenothiazine and the like. Examples of an anti-rust agent include paraffin oxide, a metal salt of carboxylic acids, carboxylic acid ester, sulphonic acid ester, salicylic acid ester, succinic acid ester, sorbitan ester and other various amine salts. Examples of an oiliness improver, extreme pressure additive and anti-wear agent include sulphurised zinc dialkyl dithiophosphate, sulphurised zinc diallyl dithiophosphate, sulphurised zinc dialkyl dithiocarbamate, sulphurised zinc diallyl dithiocarbamate, sulphurised molybdenum dialkyl dithiophosphate, sulphurised molybdenum diallyl dithiophosphate, sulphurised molybdenum dialkyl dithiocarbamate, sulphurised molybdenum diallyl dithiocarbamate, an organic molybdenum complex, a sulphurised olefin, triphenyl phosphate, triphenyl phosphorothionate, tricresine phosphate, other phosphate esters, sulphurised fats and oils and the like. Examples of a solid lubricant include molybdenum disulphide, graphite, boron nitride, melamine cyanurate, PTFE (polytetrafluoroethylene), tungsten disulphide, graphite fluoride and the like. Examples of a metal deactivator include N,N′-disalicylidene-1,2-diaminopropane, benzotriazole, benzimidazole, benzothiazole, thiadiazole and the like. Examples of a polymer include polybutene, polyisobutene, polyisobutylene, polyisoprene, polymethacrylate and the like. Examples of a metal-based cleaner include metal sulphonate, metal salicylate, metal phenate and the like. Examples of a non-metallic cleaner include succinic acid imide and the like.

Grease Composition (Blended Amount of Each Component)

Next, the blended amount for the grease composition according to the present embodiment will be described.

Base Oil

The blended amount of base oil is preferably 50 to 95 parts by mass, more preferably 60 to 90 parts by mass, even more preferably 70 to 85 parts by mass, with respect to 100 parts by mass of the total grease composition.

Thickener (Lithium-Containing Calcium Complex Soap)

The lithium-containing calcium complex soap as the thickener may be blended in an amount of preferably 1 to 40 parts by mass, more preferably 3 to 25 parts by mass, even more preferably 5 to 20 parts by mass, particularly preferably 15 to 20 parts by mass in terms of a starting material base, with respect to 100 parts by mass of the total grease composition.

The higher fatty acid in the lithium-containing calcium complex soap may be blended in an amount of 1 to 30 parts by mass, more preferably 3 to 25 parts by mass, even more preferably 5 to 20 parts by mass, with respect to 100 parts by mass of the entire grease composition.

The aromatic monocarboxylic acid in the lithium-containing calcium complex soap may be blended in an amount of 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, even more preferably 0.75 to 2.5 parts by mass, with respect to 100 parts by mass of the total grease composition.

The lower fatty acid in the lithium-containing calcium complex soap may be blended in an amount of 0.15 to 7 parts by mass, more preferably 0.5 to 6 parts by mass, even more preferably 1 to 5 parts by mass, particularly preferably 2 to 4 parts by mass, with respect to 100 parts by mass of the total grease composition.

The calcium content in the lithium-containing calcium complex soap is 3 to 15 parts by mass, more preferably 5 to 14 parts by mass, even more preferably 8 to 12 parts by mass, with respect to 100 parts by mass of the total thickener starting materials.

The lithium content in the lithium-containing calcium complex soap is 0.05 to 1 parts by mass, more preferably 0.1 to 0.6 parts by mass, even more preferably 0.15 to 0.5 parts by mass, with respect to 100 parts by mass of the total thickener starting materials.

The mass ratio of the lithium-containing calcium complex soap to the base oil is preferably about 99:1 to 60:40, more preferably about 95:5 to 65:35, even more preferably about 90:10 to 70:30.

The mass ratio of the higher fatty acid to the total carboxylic acid amount is preferably about 50 to 90%, more preferably about 60 to 80%, even more preferably about 65 to 75%.

The mass ratio of the aromatic monocarboxylic acid to the total carboxylic acid amount is preferably about 1 to 30%, more preferably about 3 to 20%, even more preferably about 5 to 15%. It is thought that with an aromatic monocarboxylic acid ratio of greater than 30%, a grease form cannot be obtained, and with a ratio of less than 1%, thermal resistance cannot be provided.

The mass ratio of the lower fatty acid to the total carboxylic acid amount is preferably about 7 to 35%, more preferably about 10 to 30%, even more preferably about 15 to 25%. It is thought that with a lower fatty acid ratio of greater than 35%, a grease form cannot be obtained, and with a ratio of less than 7%, thermal resistance cannot be provided.

The mass ratio of the aromatic monocarboxylic acid to the higher fatty acid is preferably about 3:97 to 30:70, more preferably about 5:95 to 25:75, even more preferably about 7:93 to 16:84. It is thought that when the aromatic monocarboxylic acid ratio based on the sum amount of higher fatty acid and aromatic monocarboxylic acid is greater than 30%, a grease form cannot be obtained, and when the ratio is less than 3%, thermal resistance cannot be provided.

The mass ratio of the higher fatty acid to the lower fatty acid is preferably about 85:15 to 65:35, more preferably about 83:17 to 70:30, even more preferably about 81:19 to 76:24. It is thought that when the lower fatty acid ratio based on the sum amount of higher fatty acid and lower fatty acid is greater than 35%, a grease form cannot be obtained, and when the ratio is less than 15%, thermal resistance cannot be provided.

The mass ratio of the lower fatty acid to the aromatic monocarboxylic acid is preferably about 55:45 to 15:85, more preferably about 50:50 to 20:80, even more preferably about 45:55 to 23:77. It is thought that when the lower fatty acid ratio based on the sum amount of aromatic monocarboxylic acid and lower fatty acid is greater than 90 mass %, a weak thickening effect is produced and a grease form cannot be obtained.

The mass ratio (Li/Ca) of the lithium metal content to the calcium metal content in the thickening agent starting material is preferably about 0.3 parts per 100 to 10 parts per 100, more preferably about 0.5 parts per 100 to 7 parts per 100, even more preferably about 1 part per 100 to 5 parts per 100. Herein, when the numerical value is less than 0.3 parts per 100, there is no improvement in thermal resistance or shear stability, and extension of bearing life at high temperature cannot be expected, so is not preferable. When the numerical value is greater than 10 parts per 100, the grease softens and the feeling of body is lost, and then poor rolling stability (shear stability) is produced; it is therefore not preferable.

Method for Producing the Grease Composition

The grease composition of the present embodiment may be produced according to a method generally used for producing grease. The production method is not particularly limited, and an example includes a method which involves mixing base oil, a higher fatty acid, a lower fatty acid and an aromatic monocarboxylic acid in a grease manufacturing vessel, and dissolving the contents at a temperature between 60 and 120° C. Herein, subsequently, calcium hydroxide and lithium hydroxide which are preliminarily dissolved and dispersed in an appropriate amount of distilled water are charged into the vessel. Various carboxylic acids undergo a saponification reaction with basic calcium and basic lithium (typically, calcium hydroxide and lithium hydroxide), soap slowly forms in the base oil, and the resulting product is further heated and dehydrated in order to form a grease thickener. After the completion of dehydration, the resulting product is heated to a temperature higher than 200° C., thoroughly stirred and mixed, and cooled down to room temperature. Thereafter, a mill (for example, a three-roll mill, etc.) is used in order to obtain a uniform grease composition.

Properties of the Grease Composition Dropping Point

For the grease composition of the invention, a composition having a dropping point equal to or higher than 180° C. is preferably used, a composition having a dropping point equal to or higher than 220° C. is more preferably used, and a composition having a dropping point equal to or higher than 260° C. is particularly preferably used. It is thought that when the dropping point of the grease composition is 180° C. or higher (it is usually a temperature which is at least 50° C. higher than that of calcium grease), the possibility that lubrication problems will be produced, for example, loss of viscosity at high temperature and leakage caused therefrom, burns and the like, can be suppressed. The dropping point herein refers to the temperature at which viscous grease loses the thickener configuration with increase in temperature. Herein, the dropping point is measured according to JIS K 2220 8.

Consistency

The consistency of the grease of the present embodiment is preferably Nos. 1 to 4 (175 to 340), more preferably Nos. 2 to 3 (220 to 295) according to the consistency test. The consistency indicates the apparent grease hardness. The consistency is measured by carrying out worked penetration measurements according to JIS K 2220 7.

Thermal Stability

The grease composition of the present embodiment preferably shows an evaporation loss of less than 5% based on the thin film oven test (at 150° C. for 24 hours). The thin film oven test method is described as follows. That is, 3.0 g+/−0.1 g of a sample is applied to the central area portion (50 mm×70 mm) on one side of the test piece which is the SPCC steel sheet described in the humidity cabinet test according to JIS K 2246 which has dimensions of 1.0 mm thickness×60 mm length×80 mm width, the heat test is carried out at 150° C. for 24 hours, the weight of the SPCC steel sheet before and after the heat test is respectively measured, and the evaporation amount is determined using the formula shown below. For the thin film oven test, 0.5 parts by mass of p,p′-dioctyldiphenylamine is added to 99.5 parts by mass of each grease composition of Examples 1 to 6 and Comparative Examples 1 to 4 based on 100 parts by mass of the total blended amount in the grease composition, and the test is carried out.

Evaporation amount(%)={(weight before the heat test in g−weight after the heat test in g)/weight before the heat test in g}×100

Oxidation Stability

For the grease composition of the present embodiment, the oxygen pressure loss due to an oxidation reaction according to an oxidation stability test (99° C., 100 hours) is preferably 40 kPa or less, more preferably 30 kPa, and even more preferably 20 kPa or less. The oxidation stability of grease refers to the resistance to oxidation of grease caused by a reaction with oxygen in air. The grease composition deterioration due to oxidation has an influence on base oil, and in particular, has a great influence on oxidative decomposition of a thickener. The basic function of a thickener is to hold the base oil and maintain the physical hardness of the grease in order to allow the base oil to stay on the lubrication part of a machine, and at the same time, the thickener plays a role in appropriately supplying the base oil component held by the thickener to sliding faces. When this thickener is destroyed by oxidation, the hardness originally possessed by the grease cannot be maintained and the ability to hold the base oil is lost, which base oil then slides off the lubrication part, and a suitable lubrication status cannot be maintained. This occurrence is greatly influenced by usage environment, and in particular, oxidative degradation accelerates with the increase in temperature. When oxidation of the grease progresses due to heat, an oxidation product forms, and an increase in viscosity of the base oil content, formation of sludge, destruction of network structure and the like occur, which cause hardening or softening of the grease and cause it to reach the end of its lubrication life. Use of such grease in machines may finally develop into a reduction in the service life of the machines or loss of operative reliability. Therefore, the high oxidation stability of the grease composition is extremely important in order for the lubrication part to maintain a suitable lubrication status and to improve the lubrication life. Herein, the oxidation stability is measured according to JIS2220 12.

Shear Stability

The grease consistency of the grease composition of the present embodiment after the rolling stability test (room temperature, 24 hours) is preferably 340 or less, more preferably 330 or less, even more preferably 320 or less. The rolling stability test is used to evaluate the shear stability of the grease by measuring the consistency (hardness) of the grease after kneading 50 g of test grease with the device for a predetermined period of time. The shear stability of the grease composition is an important element for maintaining the lubrication ability and physical behaviour of the grease. Poor shear stability causes grease to readily escape from the lubrication part of machine, and the required lubrication cannot be provided, which results in shortening of life, and also scattering of grease may occur which pollutes the surrounding area of the machine and impairs the working environment. Herein, the rolling stability test which is used to evaluate the shear stability is carried out according to ASTMD 1831.

Bearing Life

For the grease composition of the present embodiment, the life according to a grease bearing life test (150° C.) is preferably 200 hours or longer, more preferably 300 hours or longer, even more preferably 400 hours or longer. For the bearing life test, 6.0 g of test grease is provided to a 6306 deep-groove radial ball bearing and the test grease-placed bearing is operated with a cycle of 20 hours operation and 4 hours rest at a temperature of 150° C. The device has a mechanism wherein it stops when the power current of the motor that drives the bearing exceeds a certain level due to the subsequent loss of lubrication function of the grease and the consequent occurrence of poor bearing rotation. The time at which the device stops is read and recorded as the life of the grease. The lubrication life of grease has a great impact on the physical behaviour of grease and on chemical deterioration, and loss in either function has a great impact on the lubrication life. For example, when grease turns into a liquid at high temperature or softens a lot due to shear in the bearing, grease escapes and is lost from the bearing and the lubricating oil supplementation is not achieved, which then results in shortening of life. In addition, when there is an excessive self-heating of grease or the usage environment uses a high temperature, the grease is greatly affected by the heat and oxidation degradation progresses, and accordingly an increase in viscosity of the base oil content, a formation of sludge or a change in the thickener structure causes hardening or softening of the grease and an early end to its lubrication life. Therefore, higher machine reliability and an extension of the maintaining period can be expected with grease having a long lubrication life which has the physical behaviour of grease and allows reduced chemical deterioration and maintains stable lubrication status. Also, since the grease can also be used in a high temperature environment, it will be widely required in the market. Herein, the grease lubrication life is measured according to bearing life test ASTMD1741.

Use of the Grease Composition

The grease composition of the present embodiment can, of course, be used for generally used machines, bearings, gears and the like, and exhibits excellent performance under severe conditions, for example, under high temperature conditions. For example, the grease composition may be preferably used for lubrication of various components in automobiles such as engine peripherals including the starter, alternator and various actuators, the powertrain including the propeller shaft, constant velocity joint (CVJ), wheel bearing and clutch, the electric power steering (EPS), brake unit, ball joint, door hinge, steering wheel, cooling fan motor, brake expander and the like. In addition, the grease composition may also be preferably used in various high temperature/heavy duty parts in construction machinery such as a power shovel, bulldozer and crane truck, the steel industry, the papermaking industry, forestry machines, agricultural machines, chemical plants, power-generating facilities, drying furnaces, copying machines, railway vehicles, screw joints of seamless pipes and the like. For other purposes, the composition may also be preferably used for hard disk bearings, plastic lubrication, cartridge grease and the like.

Next, the present invention will be described in more detail by way of Examples and Comparative Examples, although the present invention is not limited by these in any way.

Starting Materials Used in the Present Composition

The starting materials used in the present Examples and Comparative examples are as follows. Unless otherwise particularly mentioned, the quantities shown in Table 1A were used for Examples 1 to 6 and in Table 1B for Comparative Examples 1 to 4. The amount of starting materials shown in Table 1 {in particular, calcium hydroxide, lithium hydroxide and various carboxylic acids (higher fatty acid, aromatic monocarboxylic acid and lower fatty acid)} is the amount of reagent. Therefore, the actual component amount in the composition can be calculated on the basis of the numerical values in Tables 1A and 1B and the purity described below.

Thickener Starting Material

Calcium hydroxide: special grade reagent having a purity of 96.0%

Lithium hydroxide: lithium hydroxide monohydrate of special grade reagent having a purity of 98.0%

Stearic acid: C18 straight-chain alkyl saturated fatty acid, which was provided as a special grade reagent having a purity of 95.0%

Behenic acid: C22 straight-chain alkyl saturated fatty acid, which was provided as a reagent having a purity of 99.0%

Benzoic acid: special grade reagent having a purity of 99.5%

Para-toluic acid: benzoic acid in which the hydrogen at p-position is substituted with a methyl group, which was provided as a special grade reagent having a purity of 98.0%

Acetic acid: alkyl fatty acid having 2 carbon atoms, which was provided as a special grade reagent having a purity of 99.7%

Butyric acid: alkyl fatty acid having 4 carbon atoms, which was provided as a special grade reagent having a purity of 98.0%

Formic acid: alkyl fatty acid having 1 carbon atom, which was provided as a special grade reagent having a purity of 98.0%

Base Oils A to D

Base oil A: paraffin-based mineral oil obtained by dewaxing solvent refinement, belongs to Group 1, the kinetic viscosity at 100° C. was 11.25 mm²/s, and the viscosity index was 97

Base oil B: poly-α-olefin, belongs to Group 4, the kinetic viscosity at 100° C. was 6.34 mm²/s, and the viscosity index was 136

Base oil C: paraffin-based mineral oil manufactured by high hydrogenation refinement, belongs to Group 3, the kinetic viscosity at 100° C. was 7.603 mm²/s, and the viscosity index was 128

Base oil D: GTL (gas to liquid) oil synthesised by the Fischer-Tropsch process, belongs to Group 3, the kinetic viscosity at 100° C. was 7.77 mm²/s, kinetic viscosity at 40° C. was 43.88 mm²/s, and the viscosity index was 148

Example 1

Starting materials, which were the base oil A, stearic acid, benzoic acid and acetic acid, were mixed in a grease manufacturing vessel, and the mixture was heated to 90° C. and the contents were dissolved. Next, calcium hydroxide and lithium hydroxide which were preliminarily dissolved and dispersed in an appropriate amount of distilled water were charged into the vessel. At this time, various carboxylic acids underwent a saponification reaction with the calcium hydroxide and lithium hydroxide, soap was slowly formed in the base oil, and the resulting product was further heated and dehydrated in order to form a grease thickener. After the completion of dehydration, the grease was heated to a temperature higher than 200° C., thoroughly stirred and mixed, and cooled down to room temperature. Thereafter, a three-roll mill was used in order to obtain uniform grease having No. 2.5 consistency.

Example 2

Starting materials, which were the base oil A, stearic acid, p-toluic acid and acetic acid, were mixed in a grease manufacturing vessel and uniform grease having No. 3 consistency was obtained in the same manner as in Example 1.

Example 3

Starting materials, which were the base oil A, behenic acid, benzoic acid and acetic acid, were mixed in a grease manufacturing vessel and uniform grease having No. 3 consistency was obtained in the same manner as in Example 1.

Example 4

Starting materials, which were a mixed oil obtained by mixing the base oils A, B, C and D, behenic acid, benzoic acid and acetic acid, were mixed in a grease manufacturing vessel and uniform grease having No. 3 consistency was obtained in the same manner as in Example 1.

Example 5

Starting materials, which were the base oil A, behenic acid, benzoic acid and acetic acid, were mixed in a grease manufacturing vessel and uniform grease having No. 2 consistency was obtained in the same manner as in Example 1.

Example 6

Starting materials, which were the base oil A, behenic acid, benzoic acid and butyric acid, were mixed in a grease manufacturing vessel and uniform grease having No. 2.5 consistency was obtained in the same manner as in Example 1.

Comparative Example 1

Starting materials, which were the base oil C, stearic acid, benzoic acid and acetic acid, were mixed in a grease manufacturing vessel, and the mixture was heated to 90° C. and the contents were dissolved. Next, calcium hydroxide which was preliminarily dissolved and dispersed in an appropriate amount of distilled water was charged into the vessel. At this time, various carboxylic acids underwent a saponification reaction with the calcium hydroxide, soap was slowly formed in the base oil, and the resulting product was further heated and dehydrated in order to form a grease thickener. After the completion of dehydration, the grease was heated to a temperature higher than 200° C., thoroughly stirred and mixed, and cooled down to room temperature. Thereafter, a three-roll mill was used in order to obtain uniform grease having No. 2 consistency.

Comparative Example 2

Starting materials, which were the base oil A, stearic acid, p-toluic acid and acetic acid, were mixed in a grease manufacturing vessel and uniform grease having No. 1.5 consistency was obtained in the same manner as in Comparative Example 1.

Comparative Example 3

Starting materials, which were the base oil A, stearic acid, benzoic acid and formic acid, were mixed in a grease manufacturing vessel, and grease was similarly manufactured on the basis of the production method of Comparative Example 1 and using the blended amounts shown in the Table. The grease showed a separation and a fluidized substance was obtained.

Comparative Example 4

The commercially available all-purpose grease manufactured by Showa Shell Sekiyu K.K. was used. The thickener was lithium 12-hydroxystearate soap, and the base oil was mineral oil-based lubricating oil. The viscosity of the base oil at 100° C. was 12.2 mm²/s.

For the grease compositions prepared respectively using the above-mentioned starting material combination and production method, the consistency, dropping point, oxidation stability, thermal stability (thin film oven test), shear stability (rolling stability test) and bearing life were measured according to the methods previously described. The results thereof are shown in Tables 2A and 2B. In Comparative Example 3, the term “unmeasurable” indicates that since the base oil and thickener were separated and a grease structure was not obtained, the dropping point could not be measured. From the results, it was found that the grease composition according to the present embodiment exhibits low shear stability/rolling stability and significantly improved bearing life while securing a high dropping point, thermal resistance and the like. With this composition, it is possible to greatly improve the grease function and increase the reliability in improving the maintenance of machines.

TABLE 1A Examples 1 2 3 4 5 6 (a) Thickener (mass %) 3.56 4.81 3.97 3.97 3.92 3.59 Alkali Calcium hydroxide Lithium hydroxide 0.23 0.30 0.23 0.23 0.50 0.22 Higher fatty acids Stearic acid 11.15 14.14 — — — — Behenic acid — — 10.13 10.13 12.82 12.12 Content with respect to 73.31 71.81 67.22 67.22 70.87 70.42 total carboxylic acids, % Aromatic monocarboxylic acids Benzoic acid 0.96 — 1.79 1.79 2.14 2.24 p-toluic acid — 1.75 — — — — Content with respect to 6.31 8.89 11.88 11.88 11.83 13.02 total carboxylic acids, % Lower fatty acids Acetic acid 3.10 3.80 3.15 3.15 3.13 — Butyric acid — — — — — 2.85 Formic acid — — — — — — Content with respect to 20.38 19.30 20.90 20.90 17.30 16.56 total carboxylic acids, % Sum of starting materials of thickener 19.00 24.80 19.27 19.27 22.51 21.02 Element contents in starting materials of thickener Ca content (mass %) 10.14 10.49 11.14 11.14 9.42 9.24 Li content (mass %) 0.199 0.199 0.196 0.196 0.365 0.172 Proportion of Li content based on 100 of Ca content, % 1.96 1.90 1.76 1.76 3.88 1.86 (b) Base oil (mass %) 81.00 75.20 80.73 20.73 77.49 78.98 Lubricating oil A Lubricating oil B 20.00 Lubricating oil C 20.00 Lubricating oil D 20.00 Total amount of composition (mass %) 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 1B Comparative Examples 1 2 3 4 (a) Thickener (mass %) 3.99 4.33 4.35 Commercially Alkali Calcium hydroxide available lithium Lithium hydroxide — — grease Higher fatty acids Stearic acid 10.88 10.87 10.87 Behenic acid — — — Content with respect to 70.83 71.09 72.18 total carboxylic acids, % Aromatic monocarboxylic acids Benzoic acid 1.00 — 1.00 p-toluic acid — 1.00 — Content with respect to 6.51 6.54 6.64 total carboxylic acids, % Lower fatty acids Acetic acid 3.48 3.42 — Butyric acid — — — Formic acid — — 3.19 Content with respect to 22.66 22.37 21.18 total carboxylic acids, % Sum of starting materials of thickener 19.35 19.62 19.41 Element contents in starting materials of thickener Ca content (mass %) 11.15 11.94 12.12 Li content (mass %) 0 0 0.00 Proportion of Li content based on 100 of Ca content, % 0 0 0.00 (b) Base oil (mass %) 80.38 80.59 Lubricating oil A Lubricating oil B Lubricating oil C 80.65 Lubricating oil D Total amount of composition (mass %) 100.00 100.00 100.00

TABLE 2A Examples 1 2 3 4 5 6 Properties Colour Pale Pale Pale Pale Pale Pale yellow yellow yellow yellow yellow yellow Status Grease Grease Grease Grease Grease Grease form form form form form form Good texture ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ Viscosity (heaviness of body) ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ Simplicity of production (ease of dehydration etc.) ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ Consistency mixed 255 236 225 240 269 259 NLGI consistency grade No. 2.5 No. 3 No. 3 No. 3 No. 2 No. 2.5 Dropping point ° C. >260 >260 >260 >260 >260 221 Thin film oven test Evaporation loss 3.28 3.21 3.47 3.23 3.32 3.12 150° C., 24 h amount % Observation of Pale Pale Pale Pale Pale Pale grease colour yellow yellow yellow yellow yellow yellow Oxidation stability test 99° C., 100 h kPa 15 20 15 10 15 20 Rolling stability test Room 310 318 240 277 302 320 temperature, 24 h Bearing life test 150° C. Hr 520 400 620 660 480 420

TABLE 2B Comparative Examples 1 2 3 4 Properties Colour Pale Pale Pale Light yellow yellow yellow brown Status Grease Grease Separated liquid Grease form form form form Good texture ⊙ ⊙ X ⊙ Viscosity (heaviness of body) ⊙ ◯ X ◯ Simplicity of production (ease of dehydration etc.) ⊙ ◯ X ⊙ Consistency mixed 267 307 — 273 NLGI consistency grade No. 2 No. 1.5 — No. 2 Dropping point ° C. >260 >260 unmeasurable 185 Thin film oven test Evaporation loss 3.74 3.37 — 15.00 150° C., 24 h amount % Observation of Pale Light — Seal brown grease colour yellow brown Oxidation stability test 99° C., 100 h kPa 30 20 — 50 Rolling stability test Room temperature, 345 358 — 338 24 h Bearing life test 150° C. Hr 200 220 — 160 

1. A grease composition comprising: base oil; and a thickener comprising a lithium-containing calcium complex soap of: (1) a C18-22 straight-chain, substituted or unsubstituted higher fatty acid, (2) a substituted or unsubstituted aromatic monocarboxylic acid having a benzene ring, and (3) a C2-4 straight-chain saturated lower fatty acid.
 2. A grease composition according to claim 1, wherein the C18-22 straight-chain higher fatty acid in the lithium-containing calcium complex soap is present in an amount of 3 to 25 parts by mass, based on 100 parts by mass of the grease composition.
 3. A grease composition according to claim 1, wherein the C18-22 straight-chain higher fatty acid is selected from the group consisting of: stearic acid, oleic acid, 12-hydroxystearic acid, behenic acid, and a combination thereof.
 4. A grease composition according to claim 1, wherein the mass ratio (Li/Ca) of the lithium metal content to the calcium metal content in the thickener starting material is 1 part per 100 to 5 parts per
 100. 5. (canceled)
 6. A grease composition according to claim 1, wherein the C18-22 straight-chain higher fatty acid in the lithium-containing calcium complex soap is present in an amount of 5 to 20 parts by mass, based on 100 parts by mass of the grease composition.
 7. A grease composition according to claim 1, wherein the aromatic monocarboxylic acid in the lithium-containing calcium complex soap is present in an amount of 0.5 to 3 parts by mass, based on 100 parts by mass of the grease composition.
 8. A grease composition according to claim 1, wherein the aromatic monocarboxylic acid in the lithium-containing calcium complex soap is present in an amount of 0.75 to 2.5 parts by mass, based on 100 parts by mass of the grease composition.
 9. A grease composition according to claim 1, wherein the aromatic monocarboxylic acid is selected from the group consisting of: benzoic acid, p-toluic acid, and a combination thereof.
 10. A grease composition according to claim 1, wherein the straight-chain saturated lower fatty acid in the lithium-containing calcium complex soap is present in an amount of 1 to 5 parts by mass, based on 100 parts by mass of the grease composition.
 11. A grease composition according to claim 1, wherein the straight-chain saturated lower fatty acid in the lithium-containing calcium complex soap is present in an amount of 2 to 4 parts by mass, based on 100 parts by mass of the grease composition.
 12. A grease composition according to claim 1, wherein the straight-chain saturated lower fatty acid is selected from the group consisting of: acetic acid, butyric acid, and a combination thereof.
 13. A method for preparing a grease composition comprising a lithium-containing calcium complex soap, the method comprising: combining a base oil, calcium hydroxide, lithium hydroxide, and the following carboxylic acids: (1) a C18-22 straight-chain, substituted or unsubstituted higher fatty acid, (2) a substituted or unsubstituted aromatic monocarboxylic acid having a benzene ring, and (3) a C2-4 straight-chain saturated lower fatty acid.
 14. The method according to claim 13, wherein the C18-22 straight-chain higher fatty acid is present in an amount of 3 to 25 parts by mass, based on 100 parts by mass of the grease composition.
 15. The method according to claim 13, wherein the C18-22 straight-chain higher fatty acid is selected from the group consisting of: stearic acid, oleic acid, 12-hydroxystearic acid, behenic acid, and a combination thereof.
 16. The method according to claim 13, wherein the aromatic monocarboxylic acid is present in an amount of 0.5 to 3 parts by mass, based on 100 parts by mass of the grease composition.
 17. The method according to claim 13, wherein the aromatic monocarboxylic acid is selected from the group consisting of: benzoic acid, p-toluic acid, and a combination thereof.
 18. The method according to claim 13, wherein the straight-chain saturated lower fatty acid is present in an amount of 1 to 5 parts by mass, based on 100 parts by mass of the grease composition.
 19. The method according to claim 13, wherein the straight-chain saturated lower fatty acid is selected from the group consisting of: acetic acid, butyric acid, and a combination thereof. 